IB DP Chemistry - S2.4.4 Polymers- Study Notes - New Syllabus - 2026, 2027 & 2028
IB DP Chemistry – S2.4.4 Polymers- Study Notes – New Syllabus
IITian Academy excellent Study Notes and effective strategies will help you prepare for your IB DP Chemistry exam.
- IB DP Chemistry 2025 SL- IB Style Practice Questions with Answer-Topic Wise-Paper 1
- IB DP Chemistry 2025 SL- IB Style Practice Questions with Answer-Topic Wise-Paper 2
- IB DP Chemistry 2025 HL- IB Style Practice Questions with Answer-Topic Wise-Paper 1
- IB DP Chemistry 2025 HL- IB Style Practice Questions with Answer-Topic Wise-Paper 2
Structure 2.4.4 — Polymers and Their Properties
Structure 2.4.4 — Polymers and Their Properties
Polymers
Polymers are large molecules (macromolecules) made by joining many small repeating units called monomers through a chemical process called polymerization.
- Monomer: A small molecule that can bond with others to form a polymer.
- Polymer: A long-chain molecule composed of repeating monomer units.
Types of Polymers:
- Natural polymers: Found in nature (e.g. proteins, DNA, cellulose, starch, rubber).
- Synthetic polymers: Man-made (e.g. polyethene, nylon, polyester, PVC).
Common Examples:
| Polymer | Monomer | Type | Use |
|---|---|---|---|
| Polyethene | Ethene | Synthetic | Plastic bags, bottles |
| Proteins | Amino acids | Natural | Body structures, enzymes |
| Cellulose | Glucose | Natural | Plant cell walls |
| Polyvinyl chloride (PVC) | Chloroethene | Synthetic | Pipes, insulation, window frames |
Structure and Properties of Plastics
The physical properties of polymers (especially plastics) are determined by:
- Length of the polymer chains – longer chains mean stronger materials.
- Degree of cross-linking – cross-links restrict movement, making polymers stronger and more rigid.
- Type of monomer used – different functional groups change polymer behavior.
General Properties of Plastics:
- Low density – compared to metals and ceramics.
- Insoluble in water – most plastics are non-polar.
- Electrical insulators – used as coatings on wires.
- Durable and non-reactive – resists corrosion and weathering.
- Malleable – can be molded into different shapes.
- Thermal behavior – depends on polymer type:
- Thermoplastics: Soften on heating, can be reshaped (e.g. polyethene).
- Thermosetting plastics: Harden permanently when heated, cannot be reshaped (e.g. Bakelite).
Bonding and Structure:
- Polymers are held together by strong covalent bonds within the chains.
- For thermoplastics, the chains are held together by weak intermolecular forces → soft and flexible.
- For thermosets, extensive cross-linking by covalent bonds makes the structure rigid and heat-resistant.
Key Concept: Polymerization Example
Polyethene is made by addition polymerization of ethene:
The double bond breaks and forms long chains of single bonds between carbon atoms.
Conclusion: Understanding polymer structure helps explain why some plastics are soft and flexible, while others are tough and heat-resistant. Their versatility explains their wide use in everyday life and industry.
Example
Explain why polyethene is flexible while Bakelite is rigid and heat-resistant, even though both are made from covalent bonds.
▶️Answer/Explanation
Polyethene: Thermoplastic polymer. It has long chains held together by weak van der Waals forces between the chains.
- Chains can slide past each other → flexible and can be reshaped on heating.
Bakelite: Thermosetting polymer. It has a network of covalent cross-links between the chains.
- Cross-links lock the chains in place → hard, rigid, and heat-resistant.
Conclusion: The difference in intermolecular bonding explains the contrast in properties despite both being covalently bonded.
Example
Compare and explain the environmental impact of synthetic polymers like PVC and natural polymers like cellulose.
▶️Answer/Explanation
PVC (polyvinyl chloride): Synthetic polymer made from chloroethene monomers.
- Non-biodegradable → persists in the environment.
- Releases toxic gases like HCl when burned.
Cellulose: Natural polymer made from glucose monomers.
- Biodegradable → broken down by enzymes and microorganisms.
- Renewable and eco-friendly.
Conclusion: Natural polymers are more sustainable and environmentally friendly than synthetic polymers like PVC.
Example
Write the balanced polymerization equation for the formation of polyvinyl chloride (PVC) and identify the type of polymerization.
▶️Answer/Explanation
Monomer: Chloroethene (vinyl chloride), \( \text{CH}_2=\text{CHCl} \)
Polymerization reaction:
\( n\text{CH}_2=\text{CHCl} \rightarrow [-\text{CH}_2-\text{CHCl}-]_n \)
Type: Addition polymerization (double bonds open up to form single bonds).